The present invention relates generally to the supplying of a combustible fuel-air mixture to an engine and more particularly to supplying an initial charge to an engine when attempting to start that engine. Even more specifically, the present invention relates to manually operable priming arrangements for supplying such an initial charge of fuel to an engine.
Engine priming arrangements are known in degrees of sophistication ranging from physically pouring fuel from a container down a carburetor throat to rather complicated fuel injection systems, as might be encountered for a diesel engine or for a fuel injected aircraft engine. Carburetors for a conventional automobile frequently have fuel pumps integral therewith which, when actuated, squirt a small charge of fuel directly into the carburetor throat. These conventional automotive arrangements link this pump to the accelerator pedal so that the pump squirts a fuel charge into the carburetor throat when the accelerator is rapidly depressed, smoothing acceleration if the engine is running, or supplying a priming charge for starting the engine, if the engine is not running. As most drivers are well aware, such a primer pump may be actuated several times by depressing the accelerator pedal repeatedly when attempting to start the automobile in cold weather. Fuel pump arrangements of this type have been used in conjunction with smaller engines as might be encountered on lawnmowers or garden tractors, but such pump arrangements are, of course, relatively expensive and complicated, with the cost thereof not justified for smaller and highly competitive engine environments.
It is also known in the small engine carburetion art to provide priming arrangements which do not directly handle or pump the priming fuel charge. In one such "indirect" priming arrangement, the air space overlying the fuel supply in the carburetor float chamber has the pressure thereof increased by the manual operation of a primer and this pressure increase forces fuel from the float chamber through an aperture which meters the fuel flow during normal running operation and thence into a so-called nozzle tube which communicates with the Venturi region of the carburetor throat supplying the priming charge to this region. Cranking the engine then pulls air through the Venturi region to be mixed with the priming fuel charge and supplied to the engine during the starting process. While representing an improvement over the "direct" primers where a pump arrangement handles the fuel directly with the resulting problems of moving seals and material deterioration due to contact with the seals, primers where the air space over the float chamber is pressurized to induce a priming charge into the carburetor throat suffer from a number of drawbacks. The float bowl and therefore also the air space above the fuel supply therein must be reasonably large to meet the fuel requirements of the engine, provide an adequate float and space therefor, and be vented somehow to atmospheric pressure for proper operation. With these constraints a relatively large volume of air must be rapidly displaced into the region atop the fuel in the float bowl to displace sufficient fuel rapidly into the carburetor throat to effect the priming operation. Also, a charge of pure fuel is supplied to the carburetor throat with such systems, whereas some initial mixing of air and fuel prior to supplying such a mixture to the carburetor throat would be desirable in order to obtain a good combustible priming charge. Still further in such arrangements both priming and running fuel must pass through the same fuel metering aperture which leads from the fuel bowl to the fuel jet. On priming such a metering aperture necessarily limits both the quantity and force with which the priming charge is introduced.